[Nel] TCP vs. UDP

[Vincent Archer]

According to Vianney Lecroart:
> On Anarchy Online game, they only use TCP protocol between client and server
> (other commercial online game use UDP) and it seems that it causes lot of
> problem like horrible ping or connection lost:
> http://aoforums.funcom.com/showthread.php?threadid=26297


This post (and the rest of the discussion) do highlight the problems of
AO. However, only one post, in the whole thread, seems to be close to the
real "problem".

I have two friends who are playing AO together. They often experience
"bad lag" (i.e. 20-30s delays between a command and it's execution).
However, there's one strange thing during these periods of bad lag.

They still chat with each other.

And I've done checking with tcpdump: you do not talk directly between clients.
Everything goes thru the AO servers.

My guess is that their architecture is based on a front-end/zone service
model. Clients connect to a front end, and said front-end connects to a
zone service, depending on the zone you are in. This is further supported
by various analysis points during beta, notably when the zone service
crashed while I was in it (and the whole mission dungeon got resert and
randomly re-rolled), and the numerous problems people have for zoning
(zone... after a strangely fixed 45s - the default TCP connection timeout -
 you get "Area Change not initiated on server).

So you have:

Client ---- TCP ----> Front End ---- TCP ----> Zone server
                          ^                  /
                          |                 /
                          V                /
Client ---- TCP ----> Front End ---- TCP -/

which is probably the worst architecture I can imagine, specially as there
appears to be one front-end per client, and front ends closes and opens
communication to zone servers. :(

> In a first step, we would like to know your opinion about this choice. And
> in a next step, we'll do some test about ping/packet lost and so on to
> compare TCP and UDP, and we'll need your help to do that.

Packet loss is a non-sequitur under TCP. You *cannot* lose packets under TCP :)
(you lose connection first)

-- 
	Vincent Archer			Email:	archer@frmug.org

All men are mortal.  Socrates was mortal.  Therefore, all men are Socrates.
							(Woody Allen)